Serbia’s interior minister said on Thursday that Albania was “not mature enough” to join the European community, stepping up a war of words over a drone stunt that forced a soccer match between the Balkan nations to be abandoned.

Minister Nebojsa Stefanovic’s remarks cast further doubt on a scheduled visit by Albanian Prime Minister Edi Rama to Belgrade next week – the first by an Albanian leader in almost 70 years.

A remote-controlled drone trailing a flag of “Greater Albania” triggered a brawl between players and a pitch invasion by fans during a qualifying match in Belgrade on Tuesday between Serbia and Albania for the 2016 European championship.

The match was abandoned at 0-0, with each side blaming the other. Serbia summoned the Albanian ambassador on Wednesday and issued a formal protest.

The countries have long had a turbulent relationship, centred on Serbia’s majority-Albanian former province of Kosovo, which declared independence in 2008.

Serbia has pinned the blame on a cluster of Albanian fans in the VIP stand of the stadium, including the brother of Rama, who were granted entrance despite a ban on ordinary Albanian fans over security concerns.

“Statements by leaders of the Albanian government demonstrate that they knew such a provocation was being prepared”, Stefanovic said in a statement.

“If Albania believes that European values are the values of so-called ‘Greater Albania’, then the Serbian Republic cannot share them by any means, and hence we believe that they are not mature enough as a state to join the European family.”

The remarks are unlikely to please Albania, with Rama due to visit Belgrade on Oct. 22. The visit had been hailed as opening a new chapter in otherwise fraught relations. Both countries aim to one day join the European Union. Albania is already a member of NATO.

Europe’s soccer governing body, UEFA, has opened disciplinary proceedings against the football associations of both countries.